s = input().split(" ")
x1 = float(s[0])
y1 = float(s[1])
x2 = float(s[2])
y2 = float(s[3])
x3 = float(s[4])
y3 = float(s[5])
side1 = ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
side2 = ((x1 - x3) ** 2 + (y1 - y3) ** 2) ** 0.5
side3 = ((x2 - x3) ** 2 + (y2 - y3) ** 2) ** 0.5
s = (side1 + side2 + side3) / 2
area = (s * (s - side1) * (s - side2) * (s - side3)) ** 0.5
print("%.1f" % (area))